Unable to unsubscribe from 'theappnebula' subscription

Please check here:

https://nebula.org/blog/refund-and-cancellation-policy/#:~:text=You%20may%20cancel%20an%20ongoing,post%20illustrates%20this%20cancellation%20process.

You may cancel an ongoing membership at any time. To cancel an ongoing membership, access your Nebula user account and cancel your membership under the Edit Profile section. This blog post illustrates this cancellation process.